The invention relates to a method and apparatus for detecting a defective object among a plurality of objects travelling along a fixed path in a given travel direction. Such objects, for example vehicles, are bound to travel along the same lane or track, for example, in a passenger transportation system. The travelling objects may also be machine components on a machine tool or on an assembly line or the like.
It has been necessary to increase the traffic density of the individual track sections in order to satisfy the increasing requirements regarding the conveying capacity and the travelling speed of modern, track bound public transportation systems. Under such operating conditions it is essential that vehicles present on the same path section and travelling on the same lane or track are recognized in time to avoid collision.
For this purpose position locating systems have been developed to an increasing extent. In such position locating systems the individual objects such as vehicles emit signals which are received by the next following object or vehicles. In such a system, if a following vehicle does not receive a signal, such condition is interpreted as a line clear signal for the path section just ahead.
In automatic, track bound passenger traffic with very short time spaces between succeeding trains or vehicles travelling at high speed it is absolutely necessary to recognize defective vehicles in time in order to avoid accidents by preventing a collision by means of a rapid braking action. All prior art methods and devices are not quite suitable for recognizing defective, track bound objects or vehicles in a fail-safe manner. The fact that prior art systems cannot operate in a fail-safe manner is due to the function principle inherent in prior art systems. For example, the absence of a signal is not an absolutely safe indication that the path section next ahead is free because the signal may be absent due to the fact that the defective vehicle does not transmit its signal. Thus, a collision between a disabled vehicle and the next following vehicle is quite possible under such an operating condition.